Personal computer systems in general and IBM personal computers in particular have attained widespread use for providing computer power to many segments of today's modern society. Personal computer systems can usually be defined as a desk top, floor standing, or portable microcomputer that consists of a system unit having a single system processor and associated volatile and non-volatile memory, a display monitor, a keyboard, one or more diskette drives, a fixed disk storage, and an optional printer. One of the distinguishing characteristics of these systems is the use of a motherboard or system planar to electrically connect these components together. These systems are designed primarily to give independent computing power to a single user and are inexpensively priced for purchase by individuals or small businesses. Examples of such personal computer systems are IBM's PERSONAL COMPUTER AT and IBM's PERSONAL SYSTEM/2 Models 25, 30, 50, 60, 70 and 80. These systems can be classified into two general families. The first family, usually referred to as Family I Models, use a bus architecture exemplified by the IBM PERSONAL COMPUTER AT and other "IBM compatible" machines. The second family, referred to as Family II Models, use IBM's MICRO CHANNEL bus architecture exemplified by IBM's PERSONAL SYSTEM/2 Models 50 through 80. The Family I models typically have used the popular INTEL 8088 or 8086 microprocessor as the system processor. These processors have the ability to address one megabyte of memory. The Family II models typically use the high speed INTEL 80286, 80386, and 80486 microprocessors which can operate in a real mode to emulate the slower speed INTEL 8086 microprocessor or a protected mode which extends the addressing range from 1 megabyte to 4 Gigabytes for some models. In essence, the real mode feature of the 80286, 80386, and 80486 processors provide hardware compatibility with software written for the 8086 and 8088 microprocessors.
As will be appreciated, all such personal computers are provided with enclosures which serve the multiple functions of protecting operating components of the computer, providing a pleasing appearance, and shielding against undesirable emission of electromagnetic energy. With the heat generating operating components thus enclosed, it is necessary to make provision for cooling those components in order that proper functioning continues. In particular, most very large scale integrated circuits, also known as VLSI chips, used in personal computers have operating ranges of temperature within which proper operation may be expected and is often warranted by chip manufacturers. Attempted operation outside the design temperature ranges can result in failure. Accordingly, efforts have been made to assure that proper cooling occurs.
Typically, cooling strategies for personal computers have relied upon air, and increasingly on forced air flow through the computer enclosure. A usual arrangement provides a single fan, typically mounted in or adjacent the power supply for the computer, which induces a flow of air through the enclosure and particularly through the power supply which is often the principal heat source within the enclosure. Such arrangements have achieved some success when used in the environments mentioned above as typical IBM personal computers.
More recently, attention has turned to enhancing the operation of personal computers by providing for the upgrading of existing machines through replacement of processors. Thus a machine first installed with an 80286 or 80386 processor may be upgraded to use a higher speed 80386 or a 80486 processor. However, with such an upgrade comes an increased thermal load. In many environments, the increased thermal load may be such that continued operation with the upgraded processor imposes operating temperatures which rise outside the design (and warranted) ranges.